1. Field of the Invention
This invention relates to improvements in the transmission of power in mechanical devices. More specifically, it relates to the use of superior synthetic hydrocarbon fluids in apparatus in which mechanical forces are transmitted or absorbed by the fluid, e.g., in automotive transmissions, hydraulic systems, shock absorbers, hydraulic steering mechanisms, clutches and other hydraulically operated devices.
2. Description of the Prior Art
Along with the development of various mechanisms for transmitting power has arisen the need for suitable fluids which perform essential functions in the operation of these mechanisms. Operation of these complex mechanisms often requires that the fluid function in several different capacities. The fluid not only serves as a lubricant and coolant in reducing the friction and heat developed during operation of the mechanism, but also performs other key functions. In the case of automatic transmissions for automotive vehicles, for example, the fluid functions hydrokinetically in the fluid coupling or torque converter, depending upon the type of transmission, and in the hydraulic operation of the various mechanical components of the driving unit.
In most hydraulic systems the hydraulic fluid must lubricate the frictional parts of the system in addition to performing the primary function of transmitting power. The parts which are so lubricated include the frictional surfaces of the fluid pump, operating pistons, cylinders, valves and fluid motors. Many of these components are complex mechanical devices.
Conventional automatic transmissions, industrial hydraulic systems, gear reducers, and the like, generally employ functional fluids having base stocks selected from naturally occurring oils of mineral origin. It is well-known, however, that such mineral oils, even upon subsequent refining, do not possess the characteristics which enable them to perform satisfactorily in such demanding applications. Thus, it is a general practice to add small amounts of other materials to these base stocks to affect one or more of the properties thereof. Because of increasing performance requiements imposed on many functional fluids, however, it has become difficult to find additives which will still perform the functions for which they are added and yet not introduce other problems such as increasing corrosion and causing harmful deposits.
The useful life of any functional fluid can generally be adjudged on the basis of criteria such as the extent of viscosity increase, the extent of corrosion to metal surfaces in contact with the fluid, and the extent of deposits. Modern automatic transmissions are illustrative of a rigorous environment where the useful life of the working fluid is of great importance. The requirements placed on automatic transmission fluids have become more severe in recent years as the horsepower of new automobiles has increased. At the same time, there has been an effort to lengthen the recommended interval between transmission oil changes. Oxidation stability requirements have become especially critcal. Sludge and varnish formation, which are symptomatic of oxidation, create serious operating problems in the complex mechanisms of the transmission.
Modern fluids for automatic transmissions, therefore, employ highly refined mineral oil base stocks with multipurpose additive packages incorporated therein. Even the most modern formulated mineral oils, however, are often marginal in long term performance when subjected to the thermal and oxidative stresses found in today's automatic transmissions for motor vehicles.
Synthetic hydrocarbon base stocks offer the potential for creating fluids which are vastly superior to mineral oil base stocks in oxidative stability and long term performance. Many synthetic fluids however, are found to cause corrosion when brought into contact with common materials, and others have been disqualified because of unsuitable viscosity properties.
It is accordingly an object of the present invention to provide a synthetic fluid having outstanding oxidation resistance and desirable viscosity properties.
Another object of this invention is to provide an improved method of transmitting power through use of superior synthetic fluids.
Still another object of the present invention is to provide an improved method of operating an automatic transmission by the use of a synthetic hydrocarbon which has superior oxidative stability and desirable viscosity properties.